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Hurricane FLORENCE

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Hurricane Florence Discussion Number 48
NWS National Hurricane Center Miami FL AL062018
500 AM AST Tue Sep 11 2018
Recent satellite imagery shows that the eye of Florence has become
cloud filled and an earlier 0441 UTC microwave overpass revealed a
double eyewall structure. These observations suggest that an
eyewall replacement cycle is likely underway. Subjective and
objective Dvorak current intensity numbers have not changed
so the initial intensity will remain 120 kt for this advisory.
An Air Force Reserve Hurricane Hunter mission is en route to the
storm and should provide a better assessment of Florence's
structure and intensity this morning. NOAA buoy 41049 located
about 80 nmi north of the eye, has reported tropical-storm-force
winds during the last several hours and seas as high as 23 ft.
Florence's upper-level environment is predicted to remain quite
favorable while the storm traverses sea surface temperatures of
around 29C over the next 48 hours. Additional strengthening is
forecast during this time, but some fluctuations in intensity are
likely due to eyewall replacement cycles. The updated NHC intensity
forecast once again calls for additional intensification and brings
Florence to near category 5 strength within the next 24 to 36
hours. After 48 hours, a slight increase in southwesterly
shear could result in some weakening, but Florence is expected to
remain an extremely dangerous hurricane when it approaches the U.S.
coastline.
Florence has accelerated as anticipated and is now moving
west-northwestward or 290 degrees at 13 kt. The track forecast
reasoning has not changed much. A mid-level ridge to the northeast
of Bermuda is expected steer Florence quickly west-northwestward to
northwestward toward the southeast United States coast over the next
2 to 3 days. By 72 hours, a high pressure ridge building over the
Upper-Midwest and Great Lakes regions is forecast to cause a
significant reduction in Florence's forward speed and the hurricane
is predicted to meander over the eastern portions of North or South
Carolina at days 4 and 5. The ECMWF has trended slower this cycle
at days 4 and 5, and as a result the NHC forecast shows slightly
less motion at those time periods. The spread in the guidance
increases by 72 hours, with the GFS and its ensemble mean along the
right side of the guidance, while the ECMWF remains along the left
edge. It should be noted that there are still a number of ECMWF
members that are even farther left. The NHC track forecast has been
nudged to the left and is close to the TVCN consensus aid. Given the
amount of uncertainty by day 3, it is important not to focus on the
exact forecast track as average NHC errors at days 3, 4, and 5 are
about 100, 140 and 180 n mi, respectively, and dangerous hazards
will extend well away from the center. Storm Surge and Hurricane
watches have been issued for a portion of the coast of South and
North Carolina. Additional watches may be required later today.
Key Messages:
1. A life-threatening storm surge is likely along portions of the
coastlines of South Carolina, North Carolina, and Virginia, and
a Storm Surge Watch has been issued for a portion of this area.
All interests from South Carolina into the mid-Atlantic region
should ensure they have their hurricane plan in place and follow
any advice given by local officials.
2. Life-threatening freshwater flooding is likely from a prolonged
and exceptionally heavy rainfall event, which may extend inland over
the Carolinas and Mid Atlantic for hundreds of miles as Florence is
expected to slow down as it approaches the coast and moves inland.
3. Damaging hurricane-force winds are likely along portions of the
coasts of South Carolina and North Carolina, and a Hurricane Watch
has been issued for a part of this area. Damaging winds could also
spread well inland into portions of the Carolinas and Virginia.
4. Large swells affecting Bermuda and portions of the U.S. East
Coast will continue this week, resulting in life-threatening surf
and rip currents.
FORECAST POSITIONS AND MAX WINDS
INIT 11/0900Z 26.4N 64.1W 120 KT 140 MPH
12H 11/1800Z 27.2N 66.4W 125 KT 145 MPH
24H 12/0600Z 28.7N 69.4W 130 KT 150 MPH
36H 12/1800Z 30.5N 72.2W 130 KT 150 MPH
48H 13/0600Z 32.2N 74.5W 125 KT 145 MPH
72H 14/0600Z 34.3N 77.1W 115 KT 130 MPH
96H 15/0600Z 35.2N 78.0W 45 KT 50 MPH...INLAND
120H 16/0600Z 36.0N 79.0W 25 KT 30 MPH...INLAND
$$
Forecaster Brown
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